HAM-DMR: talkgroup 9 is unnecessary.

HAM-DMR

Human curiosity knows no bounds, and where there is a will, there is a way. This is often the starting point of amateur radio. Next to the hobbyist with a tall antenna mast and a big antenna in the garden, a different kind of radio amateur has emerged in recent years, curious about new technologies and communication techniques in the private and professional world. Radio amateurs have thus embraced digital DMR technology, in which conversations can be digitally encoded and sent over long distances via the worldwide Internet.

The world of talkgroups

The world currently has 3 large international DMR-based radio networks for radio amateurs: DMR-MARC as the first, mainly using Motorola equipment; DMR+ as the second network, which uses the cheaper radios of mainly Hytera; and the so-called BrandMeister network, where besides the professional brands there is also considerable room for home-built equipment and other flexible applications of DMR technology.

Each of those three networks has a similar set-up: through so-called talkgroups per part of the world, continent, language, country and region, radio amateurs can communicate with each other based on language, geographic location or interests. Depending on the national implementation of the network, a radio amateur can make international contacts simply by selecting a different talkgroup.

Those talkgroups are represented by numbers, and based on those numbers the administrators of the national networks and of the individual repeaters can decide whether a transmission on such a talkgroup is passed through on their repeaters. For example, there is a talkgroup with number “1” on DMR-MARC and DMR+ (91 on BrandMeister) that should be available worldwide. Each country also has a national group based on its country code (206 for Belgium, 204 for the Netherlands, 208 for France, …) and depending on the network, regional groups are available as well (2061 for the north of Belgium, 2081 to 2089 for 9 regional zones in France, …).

The interesting thing about these groups is that, even though you are not in France, you can still call a group such as 2083 and have a conversation with other people listening to this group, without the radio amateurs on this group actually being in that region of France. For example, talkgroup 2043 is intended for the South of the Netherlands, but a radio amateur who lives in Maastricht and is on the way to Amsterdam can choose to keep transmitting and listening on group 2043 in Amsterdam, and the local repeater in Amsterdam will pass on the conversations of group 2043 for as long as the radio amateur from Maastricht is active on that repeater.

Local

There are also talkgroups with numbers 8 and 9. These groups have a separate configuration. Talkgroup 9 is reserved on all three networks for so-called “local” conversations on the individual repeater. Conversations in that group are not routed to the rest of the network, but can only be heard on the repeater that receives the incoming communication. Talkgroup 8 is often set up so that conversations on this talkgroup are shared over only a limited number of repeaters, often based on region. A province may have 2 DMR repeaters, for example, where each repeater supports a talkgroup 9 that is not connected to the other repeaters, and a talkgroup 8 that is routed to the other repeater within the same province.

At first sight there is nothing wrong with this. People within range of the repeater can use talkgroup 9 to communicate with other radio amateurs, for example from the same club, on a single repeater, and people living in the same province can use talkgroup 8 to make contact with other residents of the same province.

The problem only arises when one of the participants in a conversation is, for example, mobile and gets out of range of the repeater. Because the conversations on group 8 are shared only to a limited extent, and on group 9 not shared over other repeaters at all, this radio amateur drives himself out of range of the ongoing conversation. In essence this is not desirable, certainly not in an international, worldwide network with worldwide available talkgroups.

Reflectors as a solution

A number of solutions were devised. Many radio amateurs interested in digital technology had already had the same experiences with D-STAR, a network technology from a particular manufacturer of radio equipment. That digital technology used so-called virtual “reflectors”: numbers that local repeaters could connect to, so that a conversation held locally was also available on this “reflector”. Another radio amateur on another repeater could then link his repeater to this reflector to follow, on his own repeater, the conversation that had started on another repeater.

The reflector technique was introduced in HAM-DMR in 2014, and many radio amateurs with D-STAR experience began to apply this technique so they could still hold their conversations beyond the range of their own repeater.

This technique does have gaps, however: when a radio amateur is about to drive out of range of his repeater, he has to find a free moment within an ongoing conversation to link the repeater to a reflector, and once out of range he also has to link the local group 9 of another repeater to that same reflector. That is a lot of actions for a mobile radio amateur. In addition, there is the risk that he does not manage to link the local group of the first repeater to the reflector in time, so that he actually drives out of range of his conversation.

Talkgroups as a solution

Of course it quickly became clear that this technique has its limits. For the classic radio amateur who finds it easier to regard 1 repeater as 1 local entity, the reflector technique is an extension of the familiar analogue logic, but DMR can do so much more, and once you as a radio amateur understand the use and concept of individual talkgroups in the network, you also understand the advantages of talkgroups more quickly.

That also explains the recent group of regional talkgroups in several countries, which are available internationally. Because they can be reached internationally, these talkgroups are often also easy to set up for “roaming” on radios that support this function (the radio automatically switches to the best reachable repeater, yet keeps the same talkgroup settings, so that a conversation continues in the same talkgroup but on another repeater, without any action from the radio amateur).

Away with group 9

With the rise of these regional talkgroups, the local talkgroups 8 and 9 on individual repeaters matter less and less, and maybe it is time to phase out these talkgroups. Because it still often happens that a few radio amateurs notice they are working on the same repeater and move to the local group 9, while listening radio amateurs are not in the same region and cannot switch to the repeater with talkgroup 9 where the conversation continues.

Conversations that currently take place on group 8 and 9, and that are not available to radio amateurs who cannot receive these repeaters directly, are best held on the respective regional talkgroups. These regional talkgroups are accessible to people who are active outside the region and want to follow the conversation.

At the end of the day, however, a sysop cannot block group 9. Group 9 is already not routed on the network, and the repeater will accept every radio amateur who starts transmitting on group 9, and transmit that signal on group 9. So it is up to the individual radio amateur to think about the impact when he or she says “come on, let’s go local on group 9”. Certainly in light of remarks that it is often quiet on the three networks.

So as a radio amateur, don’t shut yourself off: come out onto the regional or on-demand talkgroups and make the hobby more interesting for others too.